There is a need for nonshrinkable polymers to use as matrices for dental composites. The specific aims of this project are: (1) to identify and synthesize polymer systems for dental use that develop expansion and/or a minimal amount of shrinkage on curing; (2) to design polymer matrices which are acceptable for the future development of dental composite resins; (3) to satisfy the primary chemical and physical requirements of these polymer and/or copolymer systems, so that they are polymerizable in vivo, and that they are fluid mixtures at 37 degrees C; and (4) to address the secondary chemical and physical requirements in these polymer matrices, i.e., little or no water sorption or solubility; low coefficient of thermal expansion; high strength; color stability; 3- to 10-min working time; and biocompatibility. In order to accomplish the specific aims, the project will have three phases. The initial phase will involve the synthesis of three polymer systems: (1) Spiro-orthocarbonates; (2) Spirobisoxazolidines; and (3) Thiiurane ring systems. All three systems have the potential of ring opening during polymerization, thus producing slightly expanding or nonshrinkable polymers. In the second phase, the new polymer systems will be characterized for their expansion and/or shrinkage on curing. New methodology combining dynamic mechanical analysis and thermomechanical analysis will be used to determine volume changes and gelation time during curing of the polymer systems. The third phase will involve determining the physical, mechanical, and biocompatibility properties of the polymer and/or copolymer systems. Standardized ASTM and ADA test methods will be used to determine properties such as water sorption and solubility, coefficient of thermal expansion, mechanical properties, color stability, working time and biocompatibility.